Golf club head

ABSTRACT

A golf club head includes a body defining an interior cavity. The body includes a sole positioned at a bottom portion of the golf club head, a crown positioned at a top portion, and a skirt positioned around a periphery between the sole and crown. The body has a forward portion and a rearward portion. The club head includes a face positioned at the forward portion of the body. The face defines a striking surface having an ideal impact location at a golf club head origin. Some embodiments of the club head have a high moment of inertia and variable thickness face.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/863,198, filed Sep. 27, 2007, which is incorporated hereinby reference.

Other applications and patents concerning golf club heads include U.S.patent application Ser. No. 11/871,933, filed Oct. 12, 2007, U.S. patentapplication Ser. No. 11/669,891, U.S. patent application Ser. No.11/669,894, U.S. patent application Ser. No. 11/669,900, U.S. patentapplication Ser. No. 11/669,907, U.S. patent application Ser. No.11/669,910, U.S. patent application Ser. No. 11/669,916, U.S. patentapplication Ser. No. 11/669,920, U.S. patent application Ser. No.11/669,925, and U.S. patent application Ser. No. 11/669,927, all filedon Jan. 31, 2007, which are continuations of U.S. patent applicationSer. No. 11/067,475, filed Feb. 25, 2005, now U.S. Pat. No. 7,186,190,which is a continuation-in-part of U.S. patent application Ser. No.10/785,692, filed Feb. 23, 2004, now U.S. Pat. No. 7,166,040, which is acontinuation-in-part of U.S. patent application Ser. No. 10/290,817, nowU.S. Pat. No. 6,773,360. These applications are incorporated herein byreference.

FIELD

The present application concerns golf club heads, and more particularly,golf club heads that incorporate features to provide increasedforgiveness for off-center hits, among other advantages. Uniquecombinations of moments of inertia, inverted cone technology and clubhead face characteristics are described.

BACKGROUND

Golf club head manufacturers and designers are constantly looking forways to improve golf club head performance, which includes theforgiveness of the golf club head, while having an aesthetic appearance.Generally, “forgiveness” can be defined as the ability of a golf clubhead to reduce the effects of mishits, i.e., hits resulting fromstriking the golf ball at a less than an ideal impact location on thegolf club head, on the shot shape and distance of a golf ball struck theby club.

Golf club head performance can be directly affected by the moments ofinertia of the club head. A moment of inertia is the measure of a clubhead's resistance to twisting about the golf club head's center ofgravity upon impact with a golf ball. Generally, the higher the momentsof inertia of a golf club head, the less the golf club head twists atimpact with a golf ball, particularly during “off-center” impacts with agolf ball, the greater the forgiveness of the golf club head andprobability of hitting a straight golf shot. Further, higher moments ofinertia typically result in greater ball speed upon impact with the golfclub head, which can translate into increased golf shot distance.

In general, the moment of inertia of a mass about a given axis isproportional to the square of the distance of the mass away from theaxis. In other words, the greater the distance of a mass away from agiven axis, the greater the moment of inertia of the mass about thegiven axis. Accordingly, golf club head designers and manufacturers havesought to increase the moment of inertia about one or more golf clubhead axes, which are typically axes extending through the golf club headcenter of gravity, by increasing the distance of the head mass away fromthe axes of interest.

In an effort to increase the forgiveness of a golf club head, some golfclub head manufacturers have focused on the size of the golf club headstriking surface. Generally, the larger the striking surface, thegreater the forgiveness of the golf club head. However, to maintain thedurability of the striking surface, increasing the size of the strikingsurface typically requires increasing the thickness of the face, e.g.,face plate, defining the striking surface, which has a direct effect onthe Coefficient of Restitution (COR) of the striking surface, or themeasurement of the ability of the striking surface to rebound the ball,e.g., the spring-like effect of the surface. In a simplified form, theCOR may be expressed as a percentage of the speed of a golf ballimmediately after being struck by the club head divided by the speed ofthe club head upon impact with the golf ball, with the measurement ofthe golf ball speed and club head speed governed by United States GolfAssociation guidelines

United States Golf Association (USGA) regulations and constraints ongolf club head shapes, sizes and other characteristics tend to limit themoments of inertia and COR achievable by a golf club head. According tothe most recent version of the USGA regulations, golf club heads must,inter alia, be generally plain in shape, have envelope dimensions at orbelow maximum envelope dimensions (maximum height of 2.8 inches, maximumwidth of 5.0 inches and a maximum depth of 5.0 inches), and have avolume at or below a maximum head volume of 470 cm³. It should be notedthat this maximum volume constraint of 470 cm³ is well below the volumeof the maximum envelope dimensions. Note that the 470 cm³ USGA limitincludes a 10 cm³ tolerance (i.e., 460 cm³+10 cm³). Further, the USGAregulations require the COR value to be less than 0.830, or have aPendulum Characteristic Time (PCT) of less than 257 microseconds. TheCOR and PCT limits just identified each include a tolerance.

Often, golf club manufacturers are faced with the choice of increasingone performance characteristic at the expense of another. For example,to promote forgiveness, some conventional golf club heads focus onincreasing the moments of inertia at the expense of increased strikingsurface size. In these golf club heads, as much of the golf club headmass as possible is moved away from the center of gravity. However, dueto mass constraints resulting from attempting to achieve the desiredswing weight (e.g., driver club head mass typically ranges from about185 g to about 215 g) , the more mass that is distributed away from thecenter of gravity, the less mass available for the face. With less massavailable for the face, to remain within the USGA constraints governingCOR and PCT, the golf club head face thickness, and thus the club headstriking surface size, is limited. Accordingly, with these conventionalgolf club heads, the forgiveness of the heads can be increased by theincreased moments of inertia, but limited by the resulting constraintson the size of the golf club head striking surface.

Conversely, to promote forgiveness, some conventional golf club headsfocus on increasing the size of the golf club head striking surface atthe expense of increased moments of inertia, potentially alsosacrificing desired center-of-gravity (“CG”) properties. As describedabove, with conventional face designs, the larger the size of thestriking surface, the thicker and more massive the face must be tocomply with USGA constraints. With more mass dedicated to the face,there is typically more mass closer to the center of gravity, and lessmass, e.g., discretionary mass, available for moving away from thecenter of gravity. Accordingly, with these conventional golf club heads,the forgiveness of the heads can be increased by the increased strikingsurface sizes, but limited by the resulting constraints on theachievable moments of inertia.

As described above, golf club designers and manufacturers have struggledto design USGA-conforming golf club heads that have both high moments ofinertia and large striking surface sizes for improved forgiveness.

SUMMARY

This application addresses at least the foregoing and discloses, interalia, golf club heads that provide improved forgiveness.

This application describes golf club heads that include a body definingan interior cavity. The golf club heads also include a sole positionedat a bottom portion of the golf club head, a crown positioned at a topportion, and a skirt positioned around a periphery between the sole andcrown. The body has a forward portion and a rearward portion.Additionally, the golf club heads include a face positioned at theforward portion of the body, and the face defines a striking surfacehaving an ideal impact location at a golf club head origin. The headorigin includes an x-axis tangential to the face and generally parallelto the ground when the head is ideally positioned, a y-axis generallyperpendicular to the x-axis and generally parallel to the ground whenthe head is ideally positioned, and a z-axis perpendicular to both thex-axis and y-axis. The positive direction for the axis is toe-to-heel,for the y-axis is front-to-back, and for the z-axis is sole-to-crown.

According to a first aspect, this application describes golf club headsthat have a moment of inertia about a golf club head center of gravityz-axis generally parallel to the head origin z-axis greater thanapproximately 490 kg·mm². The face has a thickness along the head originx-axis between t_(min) and t_(max) for at least 50% of the x-axiscoordinates x within a first range between approximately −10 mm andapproximately −50 mm, and a second range between approximately 10 mm andapproximately 50 mm, where

t _(min)=1.6+0.002378(40−|x|)², and   (1)

t _(max)=2.5+0.002854(40−|x|)².   (2)

The thickness of a first portion of the face within at respective one ofthe first and second ranges can be at least approximately 2 mm greaterthan a second portion of the face within the respective one of the firstand second ranges.

In some instances, the thickness of the face can be between t_(min) andt_(max) for at least 80% of the x-axis coordinates x within the firstand second ranges.

Golf club heads according to the first aspect can have a moment ofinertia about a golf club head center of gravity x-axis generallyparallel to the head origin x-axis greater than approximately 280kg·mm².

Golf club heads of the first aspect can have a center of gravity with anx-axis coordinate between approximately 0.0 mm and approximately 6.0 mm,and a z-axis coordinate between approximately 0.0 mm and approximately−6.0 mm.

In some embodiments, the striking surface has an area betweenapproximately 35,000 mm² and approximately 4,500 mm².

The face can also have a thickness along the head origin z-axis, betweent_(min) and t_(max) for at least 50% of the z-axis coordinates z withina third range between approximately −10 mm and approximately −30 mm, anda fourth range between approximately 10 mm and approximately 30 mm,where

t _(min)=1.6+0.002378(40−|z|)², and   (1)

t _(max)=2.5+0.002854(40−|z|)².   (2)

According to a second aspect, this application describes golf club headsthat have a moment of inertia about a golf club head center of gravityx-axis generally parallel to the head origin x-axis greater thanapproximately 280 kg·mm². The face has a thickness along the head originz-axis between t_(min) and t_(max) for at least 50% of the z-axiscoordinates z within a first range between approximately −10 mm andapproximately −30 mm, and a second range between approximately 10 mm andapproximately 30 mm, where

t _(min)=1.6+0.002378(40−|z|)², and   (1)

t _(max)=2.5+0.002854(40−|z|)².   (2)

The thickness of a first portion of the face within at respective one ofthe first and second ranges can be at least approximately 2 mm greaterthan a second portion of the face within the respective one of the firstand second ranges for golf clubs according to the second aspect.

The thickness of the face can be between t_(min) and t_(max) for atleast 80% of the z-axis coordinates z within the first and secondranges.

The striking surface of golf clubs according to the second aspect canhave an area between approximately 3,500 mm² and approximately 4,500mm².

The face of golf clubs according to the second aspect can have athickness along the head origin x-axis, the thickness being betweent_(min) and t_(max) for at least 50% of the x-axis coordinates x withina third range between approximately −10 mm and approximately −50 mm, anda fourth range between approximately 10 mm and approximately 50 mm,where

t _(min)=1.6+0.002378(40−|x|)², and   (1)

t _(max)=2.5+0.002854(40−|x|)².   (2)

Some embodiments according to the second aspect have a moment of inertiaabout a golf club head center of gravity z-axis generally parallel tothe head origin z-axis greater than approximately 490 kg·mm². Someembodiments have a center of gravity with an x-axis coordinate betweenapproximately 0.0 mm and approximately 6.0 mm, and a z-axis coordinatebetween approximately 0.0 mm and approximately −6.0 mm.

According to a third aspect, this application describes golf club headsthat have a moment of inertia about a golf club head center of gravityz-axis generally parallel to the head origin z-axis greater thanapproximately 490 kg·mm², and a moment of inertia about a golf club headcenter of gravity x-axis generally parallel to the head origin x-axisgreater than approximately 280 kg·mm². The face has a thickness along aradial axis extending tangential to and radially outwardly away from thegolf club head origin between t_(min) and t_(max) along at least 50% ofthe distances r away from the golf club head origin along the radialaxis equal to or greater than approximately 10 mm and equal to or lessthan approximately 50 mm, where

t _(min)=1.6+0.002378(40−r)², and   (1)

t _(max)=2.5+0.002854(40−r)².   (2)

Golf club heads according to the third aspect can have a strikingsurface area between approximately 3,500 mm² and approximately 4,500mm². Golf club heads of the third aspect can have a center of gravitywith an x-axis coordinate between approximately 0.0 mm and approximately6.0 mm, and a z-axis coordinate between approximately 0.0 mm andapproximately −6.0 mm.

According to a fourth aspect, golf club heads having a moment of inertiaabout a golf club head center of gravity z-axis generally parallel tothe head origin z-axis greater than approximately 500 kg·mm² aredisclosed. The face of golf clubs heads according to the fourth aspecthas a bending stiffness along the head origin x-axis, the bendingstiffness being between BS_(min) and BS_(max) for at least 50% of thex-axis coordinates x within a first range between approximately −10 mmand approximately −50 mm, and a second range between approximately 10 mmand approximately 50 mm, where

BS _(min)=1.1·10⁵[1.6+0.002378(40−|x|)²]³, and   (1)

BS _(max)=1.1·10⁵[2.5+0.002854(40−|x|)² ]³.   (2)

In some instances according to the fourth aspect, the face has athickness along the head origin x-axis, the thickness being betweent_(min) and t_(max) for at least 50% of the x-axis coordinates x withina third range between approximately −10 mm and approximately −50 mm, anda fourth range between approximately 10 mm and approximately 50 mm,where

t _(min)=1.6+0.002378(40−|x|)², and   (1)

t _(max)=2.5+0.002854(40−|x|)².   (2)

The face can have a thickness along the head origin z-axis, thethickness being between t_(min) and t_(max) for at least 50% of thez-axis coordinates z within a third range between approximately −10 mmand approximately −30 mm, and a fourth range between approximately 10 mmand approximately 30 mm, where

t _(min)=1.6+0.002378(40−|z|)², and   (1)

t _(max)=2.5+0.002854(40−|z|)².   (2)

The striking surface can have an area between approximately 3,500 mm²and approximately 4,500 mm².

Golf club heads can have a center of gravity with an x-axis coordinatebetween approximately 0.0 mm and approximately 6.0 mm, and a z-axiscoordinate between approximately 0.0 mm and approximately −6.0 mm.

Golf club heads according to a fifth aspect have a moment of inertiaabout a golf club head center of gravity x-axis generally parallel tothe head origin x-axis greater than approximately 280 kg·mm². The facehas a bending stiffness along the head origin z-axis, the bendingstiffness being between BS_(min) and BS_(max) for at least 50% of thez-axis coordinates z within a first range between approximately −10 mmand approximately −30 mm, and a second range between approximately 10 mmand approximately 30 mm, where

BS _(min)=1.1·10⁵[1.6+0.002378(40−|z|)²]³, and   (1)

BS _(max)=1.1·10⁵[2.5+0.002854(40−|z|)²]³.   (2)

Golf club heads according to the fifth aspect can have a thickness alongthe head origin x-axis, the thickness being between t_(min) and t_(max)for at least 50% of the x-axis coordinates x within a third rangebetween approximately −10 mm and approximately −50 mm, and a fourthrange between approximately 10 mm and approximately 50 mm, where

t _(min)=1.6+0.002378(40−|x|)², and   (1)

t _(max)=2.5+0.002854(40−|x|)².   (2)

The face in some embodiments has a thickness along the head originz-axis, the thickness being between t_(min) and t_(max) for at least 50%of the z-axis coordinates z within a third range between approximately−10 mm and approximately −30 mm, and a fourth range betweenapproximately 10 mm and approximately 30 mm, where

t _(min)=1.6+0.002378(40|z|)², and   (1)

t _(max)=2.5+0.002854(40|z|)².   (2)

The striking surface can have an area between approximately 3,500 mm²and approximately 4,500 mm².

Golf club heads of the fifth aspect can have a center of gravity with anx-axis coordinate between approximately 0.0 mm and approximately 6.0 mm,and a z-axis coordinate between approximately 0.0 mm and approximately−6.0 mm.

The foregoing and other features and advantages of the golf club headwill become more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a golf club head according to a firstembodiment.

FIG. 2 is a front elevation view of the golf club head of FIG. 1.

FIG. 3 is a bottom perspective view of the golf club head of FIG. 1.

FIG. 4 is a front elevation view of the golf club head of FIG. 1 showinga golf club head origin coordinate system.

FIG. 5 is a side elevation view of the golf club head of FIG. 1 showinga center of gravity coordinate system.

FIG. 6 is a top plan view of the golf club head of FIG. 1.

FIG. 7 is a cross-sectional view of the golf club head of FIG. 1 takenalong the line 7-7 of FIG. 1.

FIG. 8 is a cross-sectional side view of the golf club head of FIG. 1taken along the line 8-8 of FIG. 2.

FIG. 9 is a rear elevation view of a striking face.

FIG. 10 is a cross-sectional side view of the striking face of FIG. 9taken along the line 10-10 of FIG. 9.

FIG. 11 is a cross-sectional side view of the striking face of FIG. 9taken along the line 11-11 of FIG. 9.

FIG. 12 is a plot of variation in striking face thickness along a clubhead origin x-axis.

FIG. 13 is a plot of variation in striking face thickness along a clubhead origin z-axis.

FIG. 14 is a plot of variation in striking face bending stiffness alonga club head origin x-axis.

FIG. 15 is a plot of variation in striking face bending stiffness alonga club head origin z-axis.

FIG. 16 is a plot of variation in ball speed loss according to strikingface impact location for different golf club head embodiments.

FIG. 17 is a side elevation view of a golf club head according to asecond embodiment.

FIG. 18 is a front elevation view of the golf club head of FIG. 17.

FIG. 19 is a bottom perspective view of the golf club head of FIG. 17.

FIG. 20 is a top plan view of the golf club head of FIG. 17.

FIG. 21 is a cross-sectional view of the golf club head of FIG. 17 takenalong the line 21-21 of FIG. 17.

FIG. 22 is a cross-sectional side view of the golf club head of FIG. 17taken along the line 22-22 of FIG. 20.

FIG. 23 is a side elevation view of a golf club head according to athird embodiment.

FIG. 24 is a bottom perspective view of the golf club head of FIG. 23.

FIG. 25 is a top plan view of the golf club head of FIG. 23.

FIG. 26 is a cross-sectional view of the golf club head of FIG. 23 takenalong the line 26-26 of FIG. 23.

FIG. 27 is a cross-sectional side view of the golf club head of FIG. 23taken along the line 27-27 of FIG. 25.

DETAILED DESCRIPTION

In the following description, certain terms may be used such as “up,”“down,”, “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,”and the like. These terms are used, where applicable, to provide someclarity of description when dealing with relative relationships,particularly with respect to the illustrated embodiments. These termsare not, however, intended to imply absolute relationships, positions,and/or orientations. For example, with respect to an object, an 37upper” surface can become a “lower” surface simply by turning the objectover. Nevertheless, it is still the same object.

As illustrated in FIGS. 1-8, a wood-type (e.g., driver or fairway wood)golf club head, such as golf club head 2, includes a hollow body 10. Thebody 10 includes a crown 12, a sole 14, a skirt 16, a striking face, orface portion, 18 defining an interior cavity 79 (see FIGS. 7-8). Thebody 10 can include a hosel 20, which defines a hosel bore 24 adapted toreceive a golf club shaft (see FIG. 6). The body 10 further includes aheel portion 26, a toe portion 28, a front portion 30, and a rearportion 32. The club head 2 also has a volume, typically measured incubic-centimeters (cm³), equal to the volumetric displacement of theclub head 2. In some implementations, the golf club head 2 has a volumebetween approximately 400 cm³ and approximately 490 cm³, and a totalmass between approximately 185 g and approximately 215 g. Referring toFIG. 1, in one specific implementation, the golf club head 2 has avolume of approximately 458 cm³ and a total mass of approximately 200 g.

The crown 12 is defined as an upper portion of the club head (1) above aperipheral outline 34 of the club head as viewed from a top-downdirection; and (2) rearwards of the topmost portion of a ball strikingsurface 22 of the striking face 18 (see FIG. 6). The striking surface 22is defined as a front or external surface of the striking face 18 and isadapted for impacting a golf ball (not shown). In several embodiments,the striking face or face portion 18 can be a striking plate attached tothe body 10 using conventional attachment techniques, such as welding,as will be described in more detail below. In some embodiments, thestriking surface 22 can have a bulge and roll curvature. For example,referring to FIGS. 5 and 6, the striking surface 22 can have a bulge androll each with a radius of approximately 305 mm.

The sole 14 is defined as a lower portion of the club head 2 extendingupwards from a lowest point of the club head when the club head isideally positioned, i.e., at a proper address position relative to agolf ball on a level surface. In some implementations, the sole 14extends approximately 50% to 60% of the distance from the lowest pointof the club head to the crown 12, which in some instances, can beapproximately 15 mm for a driver and between approximately 10 mm and 12mm for a fairway wood.

A golf club head, such as the club head 2, is at its proper addressposition when the longitudinal axis 21 of the hosel 20 or shaft issubstantially normal to the target direction and at the proper lie anglesuch that the scorelines are substantially horizontal (e.g.,approximately parallel to the ground plane 17) and the face anglerelative to target line is substantially square (e.g., the horizontalcomponent of a vector normal to the geometric center of the strikingsurface 22 substantially points towards the target line). If thefaceplate 18 does not have horizontal scorelines, then the proper lieangle is set at an approximately 60-degrees. The loft angle 15 is theangle defined between a face plane 27, defined as the plane tangent toan ideal impact location 23 on the striking surface 22, and a verticalplane 29 relative to the ground 17 when the club head 2 is at properaddress position. Lie angle 19 is the angle defined between alongitudinal axis 21 of the hosel 20 or shaft and the ground 17 when theclub head 2 is at proper address position. The ground, as used herein,is assumed to be a level plane.

The skirt 16 includes a side portion of the club head 2 between thecrown 12 and the sole 14 that extends across a periphery 34 of the clubhead, excluding the striking surface 22, from the toe portion 28, aroundthe rear portion 32, to the heel portion 26.

In the illustrated embodiment, the ideal impact location 23 of the golfclub head 2 is disposed at the geometric center of the striking surface22 (see FIG. 4). The ideal impact location 23 is typically defined asthe intersection of the midpoints of a height (H_(ss)) and width(W_(ss)) of the striking surface 22. Both H_(ss) and W_(ss) aredetermined using the striking face curve (S_(ss)). The striking facecurve is bounded on its periphery by all points where the facetransitions from a substantially uniform bulge radius (face heel-to-toeradius of curvature) and a substantially uniform roll radius (facecrown-to-sole radius of curvature) to the body (see e.g., FIG. 4). Inthe illustrated example, H_(ss) is the distance from the peripheryproximate to the sole portion of S_(ss) to the perhiphery proximate tothe crown portion of S_(ss) measured in a vertical plane (perpendicularto ground) that extends through the geometric center of the face (e.g.,this plane is substantially normal to the x-axis). Similarly, W_(ss) isthe distance from the periphery proximate to the heel portion of S_(ss)to the periphery proximate to the toe portion of S_(ss) measured in ahorizontal plane (e.g., substantially parallel to ground) that extendsthrough the geometric center of the face (e.g., this plane issubstantially normal to the z-axis). See USGA “Procedure for Measuringthe Flexibility of a Golf Clubhead,” Revision 2.0 for the methodology tomeasure the geometric center of the striking face. In someimplementations, the golf club head face, or striking surface, 22, has aheight (H_(ss)) between approximately 45 mm and approximately 65 mm, anda width (W_(ss)) between approximately 75 mm and approximately 105 mm.Referring to FIG. 4, in one specific implementation, the strikingsurface 22 has a height (H_(ss)) of approximately 52.2 mm, width(W_(ss)) of approximately 90.6 mm, and total striking surface area ofapproximately 3,929 mm².

In some embodiments, the striking face 18 is made of a compositematerial such as described in U.S. Patent Application Publication Nos.2005/0239575 and 2004/0235584, U.S. patent application Ser. No.11/642,310, and U.S. Provisional Patent Application No. 60/877,336,which are incorporated herein by reference. In other embodiments, thestriking face 18 is made from a metal alloy (e.g., titanium, steel,aluminum, and/or magnesium), ceramic material, or a combination ofcomposite, metal alloy, and/or ceramic materials.

The striking face 18 can be a striking plate having a variable thicknesssuch as described in U.S. Pat. No. 6,997,820, which is incorporatedherein by reference. For example, as shown in FIGS. 7 and 8, strikingface 18 has a thickness t defined between the striking surface 20, orexterior surface, and an interior surface 40 facing the interior cavity43 of the golf club head 2. The striking face 18 can include a centralportion 42 positioned adjacent the ideal impact location 26 on thestriking surface 20. The central portion 42 can have a substantiallyconstant thickness t. The striking face 18 also can include a divergingportion 44 extending radially outward from the central portion 42. See,for example, FIGS. 9-16. The thickness t of the diverging portion 44increases in a direction radially outward from the central portion. Thestriking face 18 includes a converging portion 46 coupled to thediverging portion 44 via a transition portion 48. The thickness t of theconverging portion 46 substantially decreases with radially outwardposition from the diverging portion 44 and transition portion 48. Incertain instances, the transition portion 48 is an apex between thediverging and converging portions 44, 46. In other implementations, thetransition portion 48 extends radially outward from the divergingportion 44 and has a substantially constant thickness t (see FIGS.9-11).

In some embodiments, the cross-sectional profile of the striking face 18along any axes extending perpendicular to the striking surface at theideal impact location 23 is substantially similar as in FIGS. 9-11.

In other embodiments, the cross-sectional profile can vary, e.g., isnon-symmetric. For example, in certain implementations, thecross-sectional profile of the striking face 18 along the head originz-axis might include central, transition, diverging and convergingportions as described above (see FIGS. 9-11 and 13). However, thecross-sectional profile of the striking face 18 along the head originx-axis can include a second diverging portion 47 extending radially fromthe converging portion 46 and coupled to the converging portion via atransition portion 49. In alternative embodiments, the cross-sectionalprofile of the striking face 18 along the head origin z-axis can includea second diverging portion extending radially from the convergingportion and coupled to the converging portion, as described above withregard to variation along the head origin x-axis.

Variation in thickness of the striking face 18 with distance from thegeometric center of the striking face along an axis can be determined.According to one representative embodiment, a minimum thickness t_(min),maximum thickness t_(max), and nominal thickness t_(nom) of the strikingface 18 along the head origin x-axis within the effective range 10mm≦|x|≦50 mm can be determined from the following equations:

t _(min)(x)=1.6+0.002378(40−x)²   (1)

t _(max)(x)=2.5+0.002854(40−x)²   (2)

t _(nom)(x)=2.05+0.002616(40−x)²   (3)

Referring to FIG. 12, the representative thickness profiles obtainedusing Equations 1-3 are shown. The effective range begins about 10 mmaway from the geometric center of the striking face 20 as the portion ofthe face 18 within the less-effective range about 0 mm≦|x|≦10 mm canhave less effect on the COR of the face. However, in certain exemplaryimplementations, the thickness t of the face 18 within theless-effective range can be between approximately 2 mm and approximately5 mm, and in some instances approximately 3 mm at the central portion42. Also shown in FIG. 12 is a thickness profile for an exemplaryembodiment of a striking face 18 that is bounded by, i.e., falls within,t_(min) and t_(max) along 100% of the effective range.

Similar to that described above, a minimum thickness t_(min), maximumthickness t_(max), and nominal thickness t_(nom) of the striking face 18along the head origin z-axis within the effective range of about 10mm≦|z|≦30 mm can be determined according to the following equations:

t _(min)(z)=1.6+0.002378(40−z)²   (4)

t _(max)(z)=2.5+0.002854(40−z)²   (5)

t _(nom)(z)=2.05+0.002616(40−z)²   (6)

Referring to FIG. 13, the representative thickness profiles obtainedusing Equations 4-6 are shown. Like the effective range along the headorigin x-axis, the effective range along the head origin z-axis beginsabout 10 mm away from the geometric center of the striking face 18 asthe portion of the face 18 within the less-effective range about 0mm≦|z|≦10 mm can have less effect on the COR of the face. Also shown inFIG. 2 is a thickness profile for an exemplary embodiment of a strikingface 18 that is bounded by, i.e., falls within, t_(min) and t_(max)along 100% of the effective range.

In some implementations, the above equations and constraints can bedefined in terms of the radial distance away from the golf club headorigin. For example, a minimum thickness t_(min), maximum thicknesst_(max), and nominal thickness t_(nom) of the striking face 18 in termsof the distance r away from the golf club head origin can be determinedaccording to the following equations:

t _(min)(r)=1.6+0.002378(40−r)²   (7)

t _(max)(r)=2.5+0.002854(40−r)²   (8)

t _(nom)(r)=2.05 +0.002616(40−r)²   (9)

where r is a distance equal to or greater than approximately 10 mm awayfrom the golf club head origin.

Compared to constant thickness faces, the nominal thickness profilesalong the x-axis and z-axis represent preferred thickness profiles forreducing the weight of the face 18, increasing the COR zone of the faceand providing larger, more forgiving faces that meet the USGA CORconstraints. The same or similar advantages can be achieved, however, bya face having thickness profiles along the x-axis and z-axis that arebounded by the minimum and maximum thickness profiles for the respectivex-axis and z-axis along a predetermined portion of the effective range.For example, according to certain implementations, the striking face 18can have a thickness profile along the origin x-axis that is bounded bythe minimum and maximum thickness profiles along at least 50% of theeffective x-axis range. Similarly, the striking face 18 can have athickness profile along the origin z-axis that is bounded by the minimumand maximum thickness profiles along at least 50% of the effectivez-axis range. In more specific implementations, the thickness profile ofthe striking face 18 is bounded by the minimum and maximum thicknessprofiles along at least 60%, 70%, 80% or 90% of the effective axisrange.

In the illustrated implementation, the face 18 of golf club head 2 has athickness profile along the x-axis (see FIG. 11) and the z-axis (seeFIG. 10). The thickness profile along the x-axis of face 18 is boundedby the minimum and maximum thickness profiles along approximately 71% ofthe effective x-axis range. Similarly, the thickness profile along thez-axis of face 18 is bounded by the minimum and maximum thicknessprofiles along approximately 65% of the effective z-axis range.

In one exemplary embodiment, the face 18 is made of an isotropicmonolithic material, such as titanium. The bending stiffness (BS) for anisotropic monolithic material is proportional to the modulus ofelasticity (E) and thickness of the material, and can be determinedaccording to the following equation:

BS=Et³   (10)

where t is the thickness of the face 18.

Assuming the modulus of elasticity of titanium is about 1.1·10⁵ (N/mm²),the minimum, maximum and nominal bending stiffness BS of the face 18along the head origin x-axis within the effective range of about 10mm≦|x|≦50 mm can be determined according to the following equations:

BS _(min)(x)=1.1·10⁵[1.6+0.002378(40−x)²]³   (1)

BS _(max)(x)=1.1·10⁵[2.5+0.002854(40−x)²]³   (12)

BS _(nom)(x)=1.1·10⁵[2.05+0.002616(40−x)²]³   (13)

Referring to FIGS. 14-15, the representative bending stiffness profilesobtained using Equations 11-13 are shown. The effective range begins 10mm away from the geometric center of the striking face 20 as the portionof the face 18 within the less-effective range 0 mm≦|x|≦10 mm has arelatively small effect on the stiffness of the face. However, incertain exemplary implementations, the bending stiffness of the face 18within the less-effective range can be between approximately 9·10⁵ N·mmand approximately 1.40·10⁷ N·mm, and in some instances approximately3.0·10⁶ N·mm at the central portion 42. Also shown in FIG. 14 is abending stiffness profile for an exemplary embodiment of a striking face18 that is bounded by BS_(min), and BS_(max) along 100% of the effectivex-axis range.

Similarly, the minimum, maximum and nominal bending stiffness BS of theface 18 along the head origin z-axis within the effective range of about10 mm≦|x|≦30 mm can be determined according to the following equations(again assuming titanium with a Young's modulus of about 1.1·10⁵ N/mm²:

BS _(min)(z)=1.1·10⁵[1.6+0.002378(40−z)²]³   (14)

BS _(max)(z)=1.1·10⁵[2.5+0.002854(40−z)²]³   (15)

BS _(nom)(z)=1.1·10⁵[2.05+0.002616(40−z)² ]³   (16)

Referring to FIG. 15, the representative bending stiffness profilesobtained using Equations 14-16 are shown. Like the effective range alongthe head origin x-axis, the effective range along the head origin z-axisbegins 10 mm away from the geometric center of the striking face 18 asthe portion of the face 18 within the less-effective range 0 mm≦|z|≦10mm has a relatively small effect on the stiffness of the face. Alsoshown in FIG._is a bending stiffness profile for an exemplary embodimentof a striking face 18 that is bounded by BS_(min) and BS_(max) along100% of the effective z-axis range.

Compared to constant thickness faces, the bending stiffness profilesalong the x-axis and z-axis represent preferred bending stiffnessprofiles for increasing the stiffness distribution for a more forgivingface. The same or similar advantages can be achieved, however, by a facehaving bending stiffness profiles along the x-axis and z-axis that arebounded by the minimum and maximum thickness profiles for the respectivex-axis and z-axis along a predetermined portion of the effective range.For example, according to certain implementations, the striking face 18can have a bending stiffness profile along the origin x-axis that isbounded by the minimum and maximum bending stiffness profiles along atleast 50% of the effective x-axis range. Similarly, the striking face 18can have a bending stiffness profile along the origin z-axis that isbounded by the minimum and maximum bending stiffness profiles along atleast 50% of the effective z-axis range. In more specificimplementations, the bending stiffness profile of the striking face 18is bounded by the minimum and maximum bending stiffness profiles alongat least 60%, 70%, 80% or 90% of the effective axis range.

As the bending stiffness profiles vary according to the thicknessprofiles, the face 18 of golf club head 2 has a bending stiffnessprofile along the x-axis that is bounded by the minimum and maximumbending stiffness profiles also along approximately 71% of the effectivex-axis range. Likewise, the bending stiffness profile along the z-axisof face 18 is bounded by the minimum and maximum bending stiffnessprofiles also along approximately 65% of the effective z-axis range.

As described above, the bending stiffness profiles shown in FIGS. 14 and15 were obtained for a golf club head having a face made from a specifictitanium alloy. However, because any golf club head falling within thepreferred bending stiffness profile ranges described above will achievethe same or similar forgiveness characteristics as the tested golf clubhead, the bending stiffness profiles in FIGS. 14 and 15 also representpreferred bending stiffness profiles for golf club heads having facesmade from materials other than the specific titanium alloy and perhapsdifferent thickness profiles. For example, a golf club head having aface made from a material other than the tested titanium alloy, such as,for example, a different titanium alloy, composite material, orcombination of both, can achieve the bending stiffness profilesrepresented in FIGS. 14 and 15, but because of the material compositionof the face, may have thickness profiles different than thoserepresented in FIGS. 14 and 15. It is recognized that even though thethickness profiles may be different, a face achieving the bendingstiffness profiles described above will provide the same or similarforgiveness characteristics as a golf club head achieving the thicknessprofiles described above with regard to a titanium face. In certainimplementations, the bending stiffness profile of a golf club head facemade from a composite material, e.g., graphite epoxy or laminatedmetals, can be obtained by summation of the thickness of the layersusing methods commonly known in lamination theory

The crown 12, sole 14, and skirt 16 can be integrally formed usingtechniques such as molding, cold forming, casting, and/or forging andthe striking face 18 can be attached to the crown, sole and skirt bymeans known in the art. For example, the striking face 18 can beattached to the body 10 as described in U.S. Patent ApplicationPublication Nos. 2005/0239575 and 2004/0235584. The body 10 can be madefrom a metal alloy (e.g., titanium, steel, aluminum, and/or magnesium),composite material, ceramic material, or any combination thereof. Thewall 72 of the golf club head 2 can be made of a thin-walledconstruction, such as described in U.S. application Ser. No. 11/067,475,filed Feb. 25, 2005, which is incorporated herein by reference. Forexample, in some implementations, the wall can have a thickness betweenapproximately 0.65 mm and approximately 0.8 mm. In one specificimplementation, the wall 72 of the crown 12 and skirt 16 has a thicknessof approximately 0.65 mm, and the wall of the sole 14 has a thickness ofapproximately 0.8 mm.

A club head origin coordinate system may be defined such that thelocation of various features of the club head (including, e.g., a clubhead center-of-gravity (CG) 50 (see FIGS. 5 and 6)) can be determined.Referring to FIGS. 4-6, a club head origin 60 is represented on clubhead 2. The club head origin 60 is positioned at the ideal impactlocation 23, or geometric center, of the striking surface 22.

Referring to FIGS. 5 and 6, the head origin coordinate system, asdefined with respect to the head origin 60, includes three axes: az-axis 65 extending through the head origin 60 in a generally verticaldirection relative to the ground 17 when the club head 2 is at theaddress position; an x-axis 70 extending through the head origin 60 in atoe-to-heel direction generally parallel to the striking surface 22,i.e., generally tangential to the striking surface 22 at the idealimpact location 23, and generally perpendicular to the z-axis 65; and ay-axis 75 extending through the head origin 60 in a front-to-backdirection and generally perpendicular to the x-axis 70 and to the z-axis65. The x-axis 70 and the y-axis 75 both extend in generally horizontaldirections relative to the ground 17 when the club head 2 is at theaddress position. The x-axis 70 extends in a positive direction from theorigin 60 to the heel 26 of the club head 2. The y-axis 75 extends in apositive direction from the origin 60 towards the rear portion 32 of theclub head 2. The z-axis 65 extends in a positive direction from theorigin 60 towards the crown 12.

In one embodiment, the golf club head can have a CG with an x-axiscoordinate between approximately 0.0 mm and approximately 6.0 mm, ay-axis coordinate between approximately 30 mm and approximately 50 mm,and a z-axis coordinate between approximately 0.0 mm and approximately−6.0 mm. Referring to FIGS. 5 and 6, in one specific implementation, theCG x-axis coordinate is approximately 1.8 mm, the CG y-axis coordinateis approximately 37.1 mm, and the CG z-axis coordinate is approximately−3.3 mm.

Referring to FIG. 4, club head 2 has a maximum club head height (H_(ch))defined as the distance between the lowest and highest points on theouter surface of the body 10 measured along an axis parallel to thez-axis when the club head 2 is at proper address position; a maximumclub head width (W_(ch)) defined as the distance between the maximumextents of the heel and toe portions 26, 28 of the body measured alongan axis parallel to the x-axis when the club head 2 is at proper addressposition; and a maximum club head depth (D_(ch)), or length, defined asthe distance between the forwardmost and rearwardmost points on thesurface of the body 10 measured along an axis parallel to the y-axiswhen the club head 2 is at proper address position. The height and widthof club head 2 is measured according to the USGA “Procedure forMeasuring the Clubhead Size of Wood Clubs” Revision 1.0. In someimplementations, the golf club head 2 has a height (H_(ch)) betweenapproximately 48 mm and approximately 72 mm, a width (W_(ch)) betweenapproximately 100 mm and approximately 130 mm, and a depth (D_(ch))between approximately 100 mm and approximately 130 mm. In one specificimplementation, the golf club head 2 has a height (H_(ch)) ofapproximately 60.7 mm, width (W_(ch)) of approximately 120.5 mm, anddepth (D_(ch)) of approximately 106.7 mm.

Referring to FIGS. 5 and 6, golf club head moments of inertia aretypically defined about three axes extending through the golf club headCG 50: (1) a CG z-axis 85 extending through the CG 50 in a generallyvertical direction relative to the ground 17 when the club head 2 is ataddress position; (2) a CG x-axis 90 extending through the CG 50 in aheel-to-toe direction generally parallel to the striking surface 22 andgenerally perpendicular to the CG z-axis 85; and (3) a CG y-axis 95extending through the CG 50 in a front-to-back direction and generallyperpendicular to the CG x-axis 90 and the CG z-axis 85. The CG x-axis 90and the CG y-axis 95 both extend in a generally horizontal directionrelative to the ground 17 when the club head 2 is at the addressposition.

A moment of inertia about the golf club head CG x-axis 90 is calculatedby the following equation

Ixx=∫(y ² +z ²)dm   (17)

where y is the distance from a golf club head CG xz-plane to aninfinitesimal mass dm and z is the distance from a golf club head CGxy-plane to the infinitesimal mass dm. The golf club head CG xz-plane isa plane defined by the golf club head CG x-axis 90 and the golf clubhead CG z-axis 85. The CG xy-plane is a plane defined by the golf clubhead CG x-axis 90 and the golf club head CG y-axis 95.

A moment of inertia about the golf club head CG z-axis 85 is calculatedby the following equation

Izz=∫(x ² +y ²)dm   (18)

where x is the distance from a golf club head CG yz-plane to aninfinitesimal mass dm and y is the distance from the golf club head CGxz-plane to the infinitesimal mass dm. The golf club head CG yz-plane isa plane defined by the golf club head CG y-axis 95 and the golf clubhead CG z-axis 85.

As the moment of inertia about the CG z-axis (Izz) is an indication ofthe ability of a golf club head to resist twisting about the CG z-axis,the moment of inertia about the CG x-axis (Ixx) is an indication of theability of the golf club head to resist twisting about the CG x-axis.The higher the moment of inertia about the CG x-axis (Ixx), the greaterthe forgiveness of the golf club head on high and low off-center impactswith a golf ball. In other words, a golf ball hit by a golf club head ona location of the striking surface 18 above the ideal impact location 23causes the golf club head to twist upwardly and the golf ball to have ahigher trajectory than desired. Similarly, a golf ball hit by a golfclub head on a location of the striking surface 18 below the idealimpact location 23 causes the golf club head to twist downwardly and thegolf ball to have a lower trajectory than desired. Increasing the momentof inertia about the CG x-axis (Ixx) reduces upward and downwardtwisting of the golf club head to reduce the negative effects of highand low off-center impacts.

Compared to relatively constant thickness face designs, the variablethickness of the striking face 18 described above facilitates (1) areduction in the mass, e.g., weight, of the face without exceeding theUSGA COR constraints to allow more discretionary weight to be positionedaway from the center of gravity for increased moments of inertia orstrategically positioned for achieving a desired center of gravitylocation; (2) an increase in the size of the striking surface to promoteforgiveness; and (3) an increase in the size of a club head COR zone,e.g., the sweet spot of the golf club head face that provides the bettergolf shot forgiveness compared to other portions of the face.

Because of the weight savings resulting from the variable thicknessstriking face 18, more discretionary weight is available to increase themoments of inertia of the golf club head 2. For example, in someimplementations, the moment of inertia about the CG z-axis (Izz) of golfclub head 2 is between approximately 490 kg·mm² and 600 kg·mm², and themoment of inertia about the CG x-axis (Ixx) of golf club head 2 isbetween approximately 280 kg·mm² and approximately 420 kg·mm². In onespecific exemplary implementation, as shown in FIG. 1, the moment ofinertia about the CG z-axis (Izz) of golf club head 2 is approximately528 kg·mm² and the moment of inertia about the CG x-axis (Ixx) of golfclub head 2 is approximately 339 kg·mm².

As described above, a variable thickness striking face, such as strikingface 18, allows the area of the striking face 20 to be increased, whilemaintaining the durability of the face and keeping the COR of the facewithin the USGA limitations. The larger the face, the more surface areaavailable to contact a golf ball, and thus the more forgiving the golfclub head. A larger striking face is one of the most important featuresof a golf club, because it is the only part of the club that makescontact with the ball. Providing a larger face minimizes the chance tohit the ball off the edge of the face (resulting in, for example, a “popup” ball trajectory). Accordingly, a larger striking face gives golfersmore confidence to swing more aggressively at the ball.

Variable thickness striking faces, such as striking face 18, increasesthe COR zone of the face to increase the forgiveness of the golf clubhead. For example, referring to FIG. 16, the forgiveness of golf clubheads having various combinations of constant and variable thicknessfaces and moments of inertia about a CG z-axis (Izz) is compared. Theballspeed of a golf ball impacted at various locations on the strikingsurface along the golf club head origin x-axis for each golf club headconfiguration is shown. Club heads that experience less ball speedreduction for off-center hits are said to promote greater forgiveness.Each golf club head had a COR of 0.820 and a head mass of 206 g and wastraveling at 109 mph at impact with the golf ball. These results arebased on modeling the club head using the commercially available finiteelement analysis tool ABAQUS. As shown, the golf club head having an Izzof 600 kg·mm² and constant thickness face has similar forgivenesscharacteristics as the golf club head having a lower Izz of 400 kg·mm²but a variable thickness face. Further, the embodiment having an Izz of600 kg·mm² and variable thickness face promotes greater forgiveness thanthe golf club head having a higher Izz of 800 kg·mm² and constantthickness face.

This is not to say that club heads with a variable thickness face plateand an Izz of 600 kg·mm² has an actual moment of inertia about thez-axis in excess of 600 kg·mm². Instead, the “feel” of the club headcompares favorably to a golf club head having the higher moment ofinertia about the z-axis. It can thus be said that a club head with avariable thickness face plate and an Izz of 600 kg·mm² has an “effectiveMOI” in excess of 800 kg·mm² when considering ball speed resulting fromoff-center hits. Club heads with actual MOI less than 600 kg·mm² (e.g.,590 kg·mm²+10 kg·mm² measurement tolerance) would actually be consideredconforming to USGA MOI rules even though the effective MOI (compared toconstant face plate thickness designs) appears to be greater than 600kg·mm².

Referring to FIGS. 17-22, and according to another exemplary embodiment,golf club head 100 has a body 110 with a crown 112, sole 114, skirt 116,and striking face 118 defining an interior cavity 157. The body 110further includes a hosel 120, heel portion 126, a toe portion 128, afront portion 130, a rear portion 132, and an internal rib 182. Thestriking face 118 includes an outwardly facing ball striking surface 122having an ideal impact location at a geometric center 123 of thestriking surface. In some implementations, the golf club head 100 has avolume between approximately 400 cm³ and approximately 490 cm³, and atotal mass between approximately 185 g and approximately 215 g.Referring to FIG. 17, in one specific implementation, the golf club head100 has a volume of approximately 454 cm³ and a total mass ofapproximately 202.8 g.

Unless otherwise noted, the general details and features of the body 110of golf club head 100 can be understood with reference to the same orsimilar features of the body 10 of golf club head 2.

In the illustrated implementation, the face 118 of golf club head 100has a thickness profile along the x-axis (see FIG. 21) and the z-axis(see FIG. 22). The thickness profile along the x-axis of face 118 isbounded by the minimum and maximum thickness profiles alongapproximately 100% of the effective x-axis range. Similarly, thethickness profile along the z-axis of face 118 is bounded by the minimumand maximum thickness profiles along approximately 100% of the effectivez-axis range.

As the bending stiffness profiles vary according to the thicknessprofiles, the face 118 of golf club head 100 has a bending stiffnessprofile along the x-axis that is bounded by the minimum and maximumbending stiffness profiles also along approximately 100% of theeffective x-axis range. Likewise, the bending stiffness profile alongthe z-axis of face 118 is bounded by the minimum and maximum bendingstiffness profiles also along approximately 100% of the effective z-axisrange.

The sole 114 extends upwardly from the lowest point of the golf clubhead 100 a shorter distance than the sole 14 of golf club head 2. Forexample, in some implementations, the sole 114 extends upwardlyapproximately 50% to 60% of the distance from the lowest point of theclub head 100 to the crown 112, which in some instances, can beapproximately 15 mm for a driver and between approximately 10 mm andapproximately 12 mm for a fairway wood. Further, the sole 114 comprisesa substantially flat portion 119 extending horizontal to the ground 117when in proper address position. In some implementations, the bottommostportion of the sole 114 extends substantially parallel to the ground 117between approximately 5% and approximately 70% of the depth (Dch) of thegolf club head 100.

Because the sole 114 of golf club head 100 is shorter than the sole 12of golf club head 2, the skirt 116 is taller, i.e., extends a greaterapproximately vertical distance, than the skirt 16 of golf club head 2.

In at least one implementation, the golf club head 100 includes a weightport 140 formed in the skirt 116 proximate the rear portion 132 of theclub head (see FIG. 12). The weight port 140 can have any of a number ofvarious configurations to receive and retain any of a number of weightsor weight assemblies, such as described in U.S. patent application Ser.Nos. 11/066,720 and 11/065,772, which are incorporated herein byreference.

In some implementations, the striking surface 122 golf club head 100 hasa height (H_(ss)) between approximately 45 mm and approximately 65 mm,and a width (W_(ss)) between approximately 75 mm and approximately 105mm. In one specific implementation, the striking face 122 has a height(H_(ss)) of approximately 54.4 mm, width (W_(ss)) of approximately 90.6mm, and total striking surface area of approximately 4,098 mm².

In one embodiment, the golf club head 100 has a CG with an x-axiscoordinate between approximately 0.0 mm and approximately 6.0 mm, ay-axis coordinate between approximately 30 mm and approximately 50 mm,and a z-axis coordinate between approximately 0.0 mm and approximately−6.0 mm. In one specific implementation, the CG x-axis coordinate isapproximately 2.0 mm, the CG y-axis coordinate is approximately 37.9 mm,and the CG z-axis coordinate is approximately −4.67 mm.

In some implementations, the golf club head 100 has a height (H_(ch))between approximately 48 mm and approximately 72 mm, a width (W_(ch))between approximately 100 mm and approximately 130 mm, and a depth(D_(ch)) between approximately 100 mm and approximately 130 mm. In onespecific implementation, the golf club head 100 has a height (H_(ch)) ofapproximately 62.2 mm, width (W_(ch)) of approximately 119.3 mm, anddepth (D_(ch)) of approximately 103.9 mm.

According to certain exemplary embodiments, the golf club head 100 has amoment of inertia about the CG z-axis (Izz) between about 490 kg·mm² andabout 600 kg·mm², and a moment of inertia about the CG x-axis (Ixx)between about 280 kg·mm² and about 420 kg·mm². In one specificimplementation, the club head 100 has a moment of inertia about the CGz-axis (Izz) of approximately 500 kg·mm² and a moment of inertia aboutthe CG x-axis (Ixx) of approximately 337 kg·mm².

Referring to FIGS. 23-27, and according to another exemplary embodiment,golf club head 200 has a body 210 with a low skirt similar to body 110of golf club head 100 and body 10 of golf club head 2. The body 210includes a crown 212, a sole 214, a skirt 216, a striking face 218defining an interior cavity 257. The body 210 further includes a hosel220, heel portion 226, toe portion 228, front portion 230, and rearportion 232. The striking face 218 includes an outwardly facing ballstriking surface 222 having an ideal impact location at a geometriccenter 223 of the striking surface. In some implementations, the golfclub head 200 has a volume between approximately 400 cm³ andapproximately 490 cm³, and a total mass between approximately 185 g andapproximately 215 g. Referring to FIG. 23, in one specificimplementation, the golf club head 200 has a volume of approximately 455cm³ and a total mass of approximately 203.9 g. In other specificimplementation, the golf club head 200 has a volume of approximately 444cm³ and a total mass of approximately 205.2 g

Unless otherwise noted, the general details and features of the body 210of golf club head 200 can be understood with reference to the same orsimilar features of the body 10 of golf club head 2 and body 110 of golfclub head 100.

In the illustrated implementation, the face 218 of golf club head 200has a thickness profile along the x-axis (see FIG. 26) and the z-axis(see FIG. 27). The thickness profile along the x-axis of face 18 isbounded by the minimum and maximum thickness profiles alongapproximately 100% of the effective x-axis range. Similarly, thethickness profile along the z-axis of face 218 is bounded by the minimumand maximum thickness profiles along approximately 100% of the effectivez-axis range.

As the bending stiffness profiles vary according to the thicknessprofiles, the face 218 of golf club head 200 has a bending stiffnessprofile along the x-axis that is bounded by the minimum and maximumbending stiffness profiles also along approximately 100% of theeffective x-axis range. Likewise, the bending stiffness profile alongthe z-axis of face 218 is bounded by the minimum and maximum bendingstiffness profiles also along approximately 100% of the effective z-axisrange.

Like sole 114 of golf club head 100, the sole 214 extends upwardlyapproximately 50% to 60% of the distance from the lowest point of theclub head 200 to the crown 212. Therefore, the skirt 216 is taller,i.e., extends a greater approximately vertical distance, than the skirt16 of golf club head 2.

In at least one implementation, and shown in FIGS. 16, 18 and 20, thegolf club head 200 includes a weight port 240 formed in the sole 114proximate the rear portion 232 of the club head. The weight port 240 canhave any of a number of various configurations to receive and retain anyof a number of weights or weight assemblies. For example, as shown, theweight port 240 extends substantially vertically from the wall 272 ofthe body 210 upwardly into the interior cavity 257.

In some implementations, the striking surface 222 golf club head 200 hasa height (H_(ss)) between approximately 45 mm and approximately 65 mm,and a width (W_(ss)) between approximately 75 mm and approximately 105mm. In one specific implementation, the striking surface 222 has aheight (H_(ss)) of approximately 53.5 mm, width (W_(ss)) ofapproximately 92.3 mm, and total striking surface area of approximately4,013 mm². In another specific implementation, the striking surface 222has a height (H_(ss)) of approximately 54.7 mm, width (W_(ss)) ofapproximately 92.3 mm, and total striking surface area of approximately4,115 mm².

In one embodiment, the golf club head 200 has a CG with an x-axiscoordinate between approximately 0.0 mm and approximately 6.0 mm, ay-axis coordinate between approximately 30 mm and approximately 50 mm,and a z-axis coordinate between approximately 0.0 mm and approximately−6.0 mm. In one specific implementation, the CG x-axis coordinate isapproximately 2.2 mm, the CG y-axis coordinate is approximately 37.9 mm,and the CG z-axis coordinate is approximately −4.3 mm. In anotherspecific implementation, the CG x-axis coordinate is approximately 2.8mm, the CG y-axis coordinate is approximately 35.8 mm, and the CG z-axiscoordinate is approximately −3.4 mm.

In some implementations, the golf club head 200 has a height (H_(ch))between approximately 48 mm and approximately 72 mm, a width (W_(ch))between approximately 100 mm and approximately 130 mm, and a depth(D_(ch)) between approximately 100 mm and approximately 130 mm. In onespecific implementation, the golf club head 200 has a height (H_(ch)) ofapproximately 62.3 mm, width (W_(ch)) of approximately 120.0 mm, anddepth (D_(ch)) of approximately 111.6 mm. In another specificimplementation, the golf club head 200 has a height (H_(ch)) ofapproximately 62.6 mm, width (W_(ch)) of approximately 121.0 mm, anddepth (D_(ch)) of approximately 107.4 mm.

The golf club head 200 can, in some implementations, have a moment ofinertia about the CG z-axis (Izz) between about 490 kg·mm² and about 600kg·mm², and a moment of inertia about the CG x-axis (Ixx) between about280 kg·mm² and about 420 kg·mm². In one specific implementation, theclub head 200 has a moment of inertia about the CG z-axis (Izz) ofapproximately 516 kg·mm² and a moment of inertia about the CG x-axis(Ixx) of approximately 354 kg·mm². In another specific implementation,the club head 200 has a moment of inertia about the CG z-axis (Izz) ofapproximately 496 kg·mm² and a moment of inertia about the CG x-axis(Ixx) of approximately 329 kg·mm².

In view of the many possible embodiments to which the principles of thedisclosed golf club head may be applied, it should be recognized thatthe illustrated embodiments are only preferred examples of the golf clubhead and should not be taken as limiting the scope of the golf clubhead. Rather, the scope of the invention is defined by the followingclaims. We therefore claim as our invention all that comes within thescope and spirit of these claims.

1. A golf club head, comprising: a body defining an interior cavity andcomprising a sole positioned at a bottom portion of the golf club head,a crown positioned at a top portion, and a skirt positioned around aperiphery between the sole and crown, wherein the body has a forwardportion and a rearward portion; and a face positioned at the forwardportion of the body, the face defining a striking surface having anideal impact location at a golf club head origin, the head originincluding an x-axis tangential to the face and generally parallel to theground when the head is ideally positioned, a y-axis generallyperpendicular to the x-axis and generally parallel to the ground whenthe head is ideally positioned, and a z-axis perpendicular to both thex-axis and y-axis; wherein the golf club head has a moment of inertiaabout a golf club head center of gravity z-axis generally parallel tothe head origin z-axis greater than approximately 490 kg·mm², andwherein the face has a thickness along the head origin x-axis, thethickness being between t_(min) and t_(max) for at least 50% of thex-axis coordinates x within a first range between approximately −10 mmand approximately −50 mm, and a second range between approximately 10 mmand approximately 50 mm, wheret _(min)=1.6+0.002378(40−|x|)², and   (1)t _(max)=2.5+0.002854(40−|x|)².   (2)
 2. The golf club head of claim 1,wherein the striking surface has an area between approximately 3,500 mmand approximately 4,500 mm².
 3. The golf club head of claim 1, whereinthe face has a thickness along the head origin z-axis, the thicknessbeing between t_(min) and t_(max) for at least 50% of the z-axiscoordinates z within a third range between approximately −10 mm andapproximately −30 mm, and a fourth range between approximately 10 mm andapproximately 30 mm, wheret _(min)=1.6+0.002378(40−|z|)² and   (1)t _(max)=2.5+0.002854(40−|z|)².   (2)
 4. The golf club head of claim 1,wherein the thickness of a first portion of the face within atrespective one of the first and second ranges is at least approximately2 mm greater than a second portion of the face within the respective oneof the first and second ranges.
 5. The golf club head of claim 1,wherein the thickness of the face is between t_(min) and t_(max) for atleast 80% of the x-axis coordinates x within the first and secondranges.
 6. The golf club head of claim 1, wherein the golf club head hasa moment of inertia about a golf club head center of gravity x-axisgenerally parallel to the head origin x-axis greater than approximately280 kg·mm².
 7. The golf club head of claim 1, wherein the golf club headhas a center of gravity with an x-axis coordinate between approximately0.0 mm and approximately 6.0 mm, and a z-axis coordinate betweenapproximately 0.0 mm and approximately −6.0 mm.
 8. A golf club head,comprising: a body defining an interior cavity and comprising a solepositioned at a bottom portion of the golf club head, a crown positionedat a top portion, and a skirt positioned around a periphery between thesole and crown, wherein the body has a forward portion and a rearwardportion; and a face positioned at the forward portion of the body, theface defining a striking surface having an ideal impact location at agolf club head origin, the head origin including an x-axis tangential tothe face and generally parallel to the ground when the head is ideallypositioned, a y-axis generally perpendicular to the x-axis and generallyparallel to the ground when the head is ideally positioned, and a z-axisperpendicular to both the x-axis and y-axis; wherein the golf club headhas a moment of inertia about a golf club head center of gravity x-axisgenerally parallel to the head origin x-axis greater than approximately280 kg mm², and wherein the face has a thickness along the head originz-axis, the thickness being between t_(min) and t_(max) for at least 50%of the z-axis coordinates z within a first range between approximately−10 mm and approximately −30 mm, and a second range betweenapproximately 10 mm and approximately 30 mm, wheret _(min)=1.6+0.002378(40−|z|)², and   (1)t _(max)=2.5+0.002854(40−|z|)².   (2)
 9. The golf club head of claim 8,wherein the striking surface has an area between approximately 3,500 mm²and approximately 4,500 mm².
 10. The golf club head of claim 8, whereinthe face has a thickness along the head origin x-axis, the thicknessbeing between t_(min) and t_(max) for at least 50% of the x-axiscoordinates x within a third range between approximately −10 mm andapproximately −50 mm, and a fourth range between approximately 10 mm andapproximately 50 mm, wheret _(min)=1.6+0.002378(40−|x|)², and   (1)t _(max)=2.5+0.002854(40−|x|)².   (2)
 11. The golf club head of claim 8,wherein the thickness of a first portion of the face within atrespective one of the first and second ranges is at least approximately2 mm greater than a second portion of the face within the respective oneof the first and second ranges.
 12. The golf club head of claim 8,wherein the thickness of the face is between t_(min) and t_(max) for atleast 80% of the z-axis coordinates z within the first and secondranges.
 13. The golf club head of claim 8, wherein the golf club headhas a moment of inertia about a golf club head center of gravity z-axisgenerally parallel to the head origin z-axis greater than approximately490 kg·mm².
 15. The golf club head of claim 8, wherein the golf clubhead has a center of gravity with an x-axis coordinate betweenapproximately 0.0 mm and approximately 6.0 mm, and a z-axis coordinatebetween approximately 0.0 mm and approximately −6.0 mm.
 15. A golf clubhead, comprising: a body defining an interior cavity and comprising asole positioned at a bottom portion of the golf club head, a crownpositioned at a top portion, and a skirt positioned around a peripherybetween the sole and crown, wherein the body has a forward portion and arearward portion; and a face positioned at the forward portion of thebody, the face defining a striking surface having an ideal impactlocation at a golf club head origin, the head origin including an x-axistangential to the face and generally parallel to the ground when thehead is ideally positioned, a y-axis generally perpendicular to thex-axis and generally parallel to the ground when the head is ideallypositioned, and a z-axis perpendicular to both the x-axis and y-axis;wherein the golf club head has a moment of inertia about a golf clubhead center of gravity z-axis generally parallel to the head originz-axis greater than approximately 490 kg·mm , and a moment of inertiaabout a golf club head center of gravity x-axis generally parallel tothe head origin x-axis greater than approximately 280 kg·mm², andwherein the face has a thickness along a radial axis extendingtangential to and radially outwardly away from the golf club headorigin, the thickness being between t_(min) and t_(max) along at least50% of the distances r away from the golf club head origin along theradial axis equal to or greater than approximately 10 mm and equal to orless than approximately 50 mm, wheret _(min)=1.6+0.002378(40−r)², and   (1)t _(max)=2.5+0.002854(40−r)².   (2)
 16. The golf club head of claim 15,wherein the striking surface has an area between approximately 3,500 mm²and approximately 4,500 mm².
 17. The golf club head of claim 15, whereinthe golf club head has a center of gravity with an x-axis coordinatebetween approximately 0.0 mm and approximately 6.0 mm, and a z-axiscoordinate between approximately 0.0 mm and approximately −6.0 mm.
 18. Agolf club head, comprising: a body defining an interior cavity andcomprising a sole positioned at a bottom portion of the golf club head,a crown positioned at a top portion, and a skirt positioned around aperiphery between the sole and crown, wherein the body has a forwardportion and a rearward portion; and a face positioned at the forwardportion of the body, the face defining a striking surface having anideal impact location at a golf club head origin, the head originincluding an x-axis tangential to the face and generally parallel to theground when the head is ideally positioned, a y-axis generallyperpendicular to the x-axis and generally parallel to the ground whenthe head is ideally positioned, and a z-axis perpendicular to both thex-axis and y-axis; wherein the golf club head has a moment of inertiaabout a golf club head center of gravity z-axis generally parallel tothe head origin z-axis greater than approximately 490 kg·mm², andwherein the face has a bending stiffness along the head origin x-axis,the bending stiffness being between BS_(min) and BS_(max) for at least50% of the x-axis coordinates x within a first range betweenapproximately −10 mm and approximately −50 mm, and a second rangebetween approximately 10 mm and approximately 50 mm, whereBS _(min)=1.1·10⁵[1.6+0.002378(40−|x|)²]³, and   (1)BS _(max)=1.1·10⁵[2.5+0.002854(40−|x|)²]³.   (2)
 19. The golf club headof claim 18, wherein the striking surface has an area betweenapproximately 3,500 mm² and approximately 4,500 mm².
 20. The golf clubhead of claim 18, wherein the golf club head has a center of gravitywith an x-axis coordinate between approximately 0.0 mm and approximately6.0 mm, and a z-axis coordinate between approximately 0.0 mm andapproximately −6.0 mm.
 21. The golf club head of claim 18, wherein theface has a thickness along the head origin x-axis, the thickness beingbetween t_(min) and t_(max) for at least 50% of the x-axis coordinates xwithin a third range between approximately −10 mm and approximately −50mm, and a fourth range between approximately 10 mm and approximately 50mm, wheret _(min)=1.6+0.002378(40−|x|)², and   (1)t _(max)=2.5+0.002854(40−|x|)².   (2)
 22. The golf club head of claim18, wherein the face has a thickness along the head origin z-axis, thethickness being between t_(min) and t_(max) for at least 50% of thez-axis coordinates z within a third range between approximately −10 mmand approximately −30 mm, and a fourth range between approximately 10 mmand approximately 30 mm, wheret _(min)=1.6+0.002378(40−|z|)² and   (1)t _(max)=2.5+0.002854(40−|z|)².   (2)
 23. A golf club head, comprising:a body defining an interior cavity and comprising a sole positioned at abottom portion of the golf club head, a crown positioned at a topportion, and a skirt positioned around a periphery between the sole andcrown, wherein the body has a forward portion and a rearward portion;and a face positioned at the forward portion of the body, the facedefining a striking surface having an ideal impact location at a golfclub head origin, the head origin including an x-axis tangential to theface and generally parallel to the ground when the head is ideallypositioned, a y-axis generally perpendicular to the x-axis and generallyparallel to the ground when the head is ideally positioned, and a z-axisperpendicular to both the x-axis and y-axis; wherein the golf club headhas a moment of inertia about a golf club head center of gravity x-axisgenerally parallel to the head origin x-axis greater than approximately280 kg·mm², and wherein the face has a bending stiffness along the headorigin z-axis, the bending stiffness being between BS_(min) and BS_(max)for at least 50% of the z-axis coordinates z within a first rangebetween approximately −10 mm and approximately −30 mm, and a secondrange between approximately 10 mm and approximately 30 mm, whereBS _(min)=1.1·10⁵[1.6+0.002378(40−|z|)²]³, and   (1)BS _(max)=1.1·10⁵[2.5+0.002854(40−|z|)²]³.   (2)
 24. The golf club headof claim 23, wherein the striking surface has an area betweenapproximately 3,500 mm² and approximately 4,500 mm².
 25. The golf clubhead of claim 23, wherein the golf club head has a center of gravitywith an x-axis coordinate between approximately 0.0 mm and approximately6.0 mm, and a z-axis coordinate between approximately 0.0 mm andapproximately −6.0 mm.
 26. The golf club head of claim 23, wherein theface has a thickness along the head origin x-axis, the thickness beingbetween t_(min) and t_(max) for at least 50% of the x-axis coordinates xwithin a third range between approximately −10 mm and approximately −50mm, and a fourth range between approximately 10 mm and approximately 50mm, wheret _(min)=1.6+0.002378(40−|x|)² , and   (1)t _(max)=2.5+0.002854(40−|x|)².   (2)
 27. The golf club head of claim23, wherein the face has a thickness along the head origin z-axis, thethickness being between t_(min) and t_(max) for at least 50% of thez-axis coordinates z within a third range between approximately −10 mmand approximately −30 mm, and a fourth range between approximately 10 mmand approximately 30 mm, wheret _(min)=1.6+0.002378(40−|z|)², and   (1)t _(max)=2.5+0.002854(40−|z|)².   (2)